Mechanism for transmitting linear or rotary movement



Sep@ E1, 1945. N. E. HEwrrT MEGHANISM FOR TRANSMITTING LINEAR OR ROTARY MOVEMENT Filed oct; 25, 194s 5 Sheets-Sheet 1 c FELPLI ii @nu ME Sept. 11, 1945. N. E, HEWlT-r 2,384,742

MECHANISM FOR TRANSMITTING LINEAR OR ROTARY MOVEMENT Filed Oct. 25, 1943 SSheets-Shee't 2 Sept. 11, 1945. N. E. HEwITT MECHANISM FOR TRANSMITTING LINEAR OR ROTARYMOVEMENT VFiled Oct. 25, 1943 3 Sheets-Sheet 3 Patented Sept. 11, 1945 MECHANISM FOR TRANSMITLING VLINEAR` R ROTARY MOVEMENT i Norman Ebenezer Hewitt, `Sunbury-on-Thames,

England Application October 25, 19443, Serial No. 507,584 In Great Britain June 26, 1942 2 Claims. (ci. v4-110) This invention relates toV mechanism for transmitting linear or rotary movement. There are various types of mechanisms in which a Wire or the like can move within a sheath so as to enable linear movement to be transmitted even with curved paths but there are many instances (especially in the adjustment of instruments, sighting devices and the like) where such types of mechanisms give rise to difficulty particularly due to lost motion and to friction. The object of this invention is to provide mechanisms which minimise lost motion and friction.

It has previously been proposed to employ a mechanism comprising a tube within which is a series of alternating metal balls and distance pieces with concave ends, the diameter of the balls being greater than the diameter of the distance pieces so that it is the balls that contact with the inner surface of the tube: it has also been proposed to use springs to maintain the series of balls and distance pieces under compression.

This invention comprises a mechanism for transmitting linear movement in both directions in which there are two parallel flexible sheaths each provided internally with a series of alternating metal balls, and distance pieces with concave ends, and in which at each end of each sheath the series is operatively connected to a lever pivoted in a casing, the sheaths being fixed against axial movement in relation to said casings so that when angular movement is imparted to the lever at one end, corresponding angular movement is transmitted to the lever at the other end and the series of balls and distance pieces in each sheath is maintained in compression.

The balls are preferably steel balls such as are used in ball-bearings but may be of non-ferrous material. The distance pieces may be simple cylinders or prisms having concave ends of the same radius of curvature as the balls with which they are in close contact. Alternatively, the distance pieces may be bobbin-shaped with a central portion in the form of a cylinder or prism and end portions of greater diameter also in the formy of cylinders or prisms, concave recesses being formed in the ends to engage the balls. The sheath preferably consists of a cylindrical metal tube which is flexible; this may be formed from braided metal Wire or better still from helical metal tape, but other forms of flexible or rigid sheath may be employed, it being important that the inner surface is smooth so that the balls may move over said inner surface with the minimum of friction (the balls normally being free to rotate during movement round a bend). Alternatively the sheath may be a skeleton tube, and of round, square or any shaped section, so long as it achieves its purpose of constraining and guiding the inner member.

In mechanism for transmitting movement (particularly for the adjustment of instruments and the like) of the type referred to above it sometimes happens that the linear movement in the transmission can be considerably greater than the linear movement required for the actual adjustment: and indeed the linear movement in the transmission can be considerably greater than the linear movement effected by the operator. If the adjustment is effected by rotation of a spindle, sleeve or like operating memberfor if the movement effected by the operator is a movement of rotation), it may be desirable that the.

angle of rotation is quite small or the rate of rotation is quite low while the linear movement in the transmission is comparatively great or rapid. Such an arrangement (involving a reducing gear) affords the advantage pointed out above that any lost motion in the coupling would be reduced in the adjustment. A further object of the present invention is to combine with a mechanism for transmitting linear motion of the type described above a reducing gear which imparts longitudinal and/or rotary movement to a spindle, sleeve or the like.

According to this invention the mechanism for transmitting linear movement comprises (as before) a sheath within which is a series of alternating metal balls and distance pieces with concave ends. There are tvvo parallel sheaths but the series of alternating balls and distance pieces in the said sheaths are not separated from one another but form one continuous series which, Within a relatively fixed casing passes around a helical channel. A shaft with its axis in the axis of the helix has screw engagement with the casing and carries a projecting arm engaging with said series (e. g. replacing one ball in the series) the arrangement being such that as the series of alternating balls and distance pieces moves in the helical channel the outer end of the arm is caused to follow in the helical path thus rotating the shaft which also moves axially, the pitch of the screw being the same as the pitch of the helix.

-Conveniently the casing contains a rotatable 5o sleeve having a longitudinal slot to accommodate the outer end of the arm and to guide it. The sleeve may carry an axial spindle making a sliding lit Within a long axial recess in the shaft so as to assist in supporting the shaft.

According to a further feature of this invention,

enlarged scale.

the mechanism for transmitting linear or rotary movement comprises (as before) a sheath within which is a series of alternating balls and distance pieces with concave ends: there are two such sheaths and the series of alternating balls and distance pieces in the said sheaths are not separated from one another, but they pass into a substantially circular channel in a relatively xed casing. A shaft with its axis normal to the plane of said channel has a radial arm which engages the series (e. g. which takes the place of one or more distance pieces), the-arrangement being such that as the series of balls and distance pieces moves in either direction, the arm rotates the shaft in the casing. It is preferable to have such a casing at each end of the sheaths so as to form a transmission system.

In the accompanying drawings which illustrate various forms of the mechanism embodying this invention:

i Figure l is an elevation `partly in section and partly with a cover plate-removed, showing one end of the mechanism and a portion of the sheath about the middle, and

Figure 2is a view mainly in section and on an Figures 3, 4, 5, 6 and 7 illustrate one form of reducing gear for use with the transmission of this invention.

i Figure 3 is a central longitudinal section of the casing, the shaft being shown in full,

Figure 4 is an end view of the casing,

Figure 5 is an end view lof the `sleeve alone,

Figure 6 is a side view, and

Figure 7 is a plan. Y

Figures 8 and 9 relate to an alternative form of this invention;

Figure 8 is a plan, partly in section, of the operating mechanism at the end rof the transmission, and

Figure 9 is a section on the line 9-9 of Figure 8; j

Referring to kFigures l vand 2, metal balls I2 alternate with distance pieces I3 with concave ends within a flexible sheath which is of a composite'character. The inner part of the sheath is 'a smooth tube of brass I4 with a helical cut I5 throughout its length so that this exible metal tube is like a flat; narrow metal tape which has been-helically ywound on a Icylindrical core.

ImmediatelyA outside ,the helical exible tube is a sheath i5 of braided wire and outside that again is a cover II of braided fabric. In the arrangement shown there are two parallelV sheaths each provided internally with a series of alternating balls I2 and distance pieces I3.

At each end of each sheath is a sliding plunger I8 contacting with the last ball and these plungers are operatively connected with a rocking lever I9 on a spindle 20 pivoted in a casing 2|, The arrangement is the same at each end of the mechanism.

In the form shown, rocking lever I3 (as above stated) has .a spindle 2) pivoted Ain Vthe casing 2I and the rocking lever has anarcuate rack 22 engaging asmall'toothed pinion 23 which is pivoted at 24 in the casing. The small pinion 23 is inpieces in each sheath is maintained in com-A pression.

The arrangement of the racks 22 and 26 and the pinions 23 and 25 constitutes a reducing gear so that any lost motion in the coupling would be reduced in the rotation of the spindle 20. The reduction can easily be 100:1 so that a lost motion of one thousandth of an inch in the coupling would be reduced to one hundred-thousandth of an inch at the instrument or sighting device which is being adjusted.

'I'he method of xing the sheaths I6 and I'I in this example is as follows:

At each end of the sheath where it embraces the sliding plunger I3 a short cylindrical metal collar 21 is rmly secured to the braided metal tegral with or secured to a largerV pinion 25 which sheath I6 and the fabric sheath I'I, and this collar is located in a cylindrical recess in the casing 2| and is iirmly held in position by a long metal sleeve 28 having a flange 29 and adjustable xing screws 30 which screwinto the bottom of the casing 2I. Y v v About the middle of the sheath as a whole a short clamping sleeve 3| embraces the sheath and is inwardly depressed as at 32 to secure the outer sheaths I 5 and I'I to the helical metal sheath I4.- It will be seen that by the arrangement described, When the sheath as a whole is bent, the outer sheaths I6 and I'l cannot move longitudinally at all but the helical metal sheath I4 can move slightly from ythe xed point 32 in relation to the outer sheaths I5 and I'I.

In another arrangement the sliding plungers I8 are not toothed but are coupled to the ends offa length of chain which in turn engages with the yteeth of a sprocket wheel which replaces the pinion 25.

In yet another arrangement, the inner member may be coupled at its end or at each end to a ilexible cable which passes around one or more wheels or drums and is secured' thereto so that motion is conveyed by or to such wheels or drums.

It is not necessary that the casing or sheath shall be a continuous tube: it may be slotted.

Referring to Figures 3 to '7, the sheaths 42 containing the series of balls and spacers are secured to a casing 43 having on its internal cylindrical surface a helical channel 44 and the series of balls and spacers passes around this channel. An axial shaft 45 carries a screw thread 46 (here shown as a 2-start thread), a boss 4l on the casing being internally threaded to correspond. The inner end of the shaft 45 has a long axial recess 48 having a sliding fit with an axial spindle 49 projecting from a rotatable sleeve 5i! having a longitudinal slot 5I in itsr cylindrical wall. A radial arm 52 projects from the innerend of the shaft 45 and passes through the longitudinal slot 5I in the sleeve 5I) which thus acts as a guide for the arm 52. The cuter end of the arm 52 is suitably shaped to engage the series of balls and spacers. For example, i1; may replace one ball. The end of the casing 43 is closed by the cover 53. The effective pitch ofthe screw 46 is the same as the pitch of the helical channel 44 and as the series of balls and spacers is movedin the channel, the'arm v52- is correspondingly moved and the sha-ft 45 is rotated and moved axially. The number of turns inthe helical channel I4 may be selected to suit the extent o1" motion required.

The rotatable sleeve 5G lying immediately within the helical channel 44 serves to maintainl ,the ballsand spacers within the helical channel.` f

Referring to Figures 8 and 9, the two sheaths 6| each containing the series of balls 62 and spacers 63 are secured (at each end of the sheaths) to a boss or Side arm 64 projecting radially from a circular casing 65. A channel 65 for balls and spacers is formed within the circular casing around the greater part of the circle (say 300) and the two ends of that circular channel lead into two channels 61 in the boss or side arm 64 so that one continuous channel or path is provided for the balls and spacers.

In the centre of the circular casing 65 there is pivoted a radial member 6B which at its outer end engages the series of balls and spacers. For example, a projection 69 from the radial member may replace part of the series. Conveniently it may replace two spacers and one ball so that each end of this projection is in contact with a ball. lTo enable the compression in the series of balls and spacers to be maintained or adjusted, the radial arm 68 and the projection 69 therefrom may be split and a manually adjustable cam 'I0 may be used for varying the distance between the two parts. It will be understood that at one end of the transmission system movement may be imparted to a spindle, sleeve or the like secured to the pivot 'Il of the radial arm and at the other end of the pivot of the radial arm may be connected to the instrument or device which is to be operated.

I claim:

1. A mechanism for transmitting linear movement in both directions having in combination two parallel flexible sheaths, a series of alternating metal balls and distance pieces with concave ends longitudinally slidably positioned in each sheath, two casings, one at each end of said sheaths, the sheaths, being Xed against aXial movement in relation to said casings, a lever pivoted in each casing, and operative connections between each lever and the appropriate ends of the two series of metal balls and distance pieces, whereby the balls and distance pieces of both series are maintained in compression, the metal balls and distance pieces forming a continuous series and each casing having a helical channel around which the series passes, each casing having a lever secured to a shaft coaxial with the helix and having screw engagement with the casing.

2. A mechanism for transmitting linear movement in both directions having in combination two parallel flexiblesheaths, a series of alternating metal balls and distance pieces with concave ends longitudinally slidably positioned in each sheath, two casings, one at each end oi said sheaths,the sheaths being xed against axial movement in relation to said casings, a lever pivoted in each casing, and operative connections between each lever and the appropriate ends of the two series of metal balls and distance pieces, whereby the balls and distance pieces of both series are maintained in compression, casings each provided with a substantially circular channel around which the series of balls and distance pieces passes, a shaft rotatably mounted in each casing normal to the plane of said channel and a radial lever secured to the shaft and engaging the series of balls and distance pieces.

NORMAN EBENEZER. HEWITT. 

